Our brains love playing tricks on us, and the results can be detrimental. Because of how we remember certain events, even a good experience can be recalled as an awful one because of one little problem. Dr. Peter Noel Murray, writing for Psychology Today, explains:

[A] consumer could have a great experience with a product or service, but only have bad memories when thinking about it later. Here's how. Let's say you are on vacation and have dinner at the best restaurant recommended to you. Perfect table. Food is exquisitely prepared. Wonderful wine. The experience is fantastic. However, when clearing the table the waiter spills coffee into your lap. Odds are that the coffee spill will degrade your memory of the food and wine, no matter how exceptional you otherwise would have remembered them. And if the hot coffee burned a leg or damaged an expensive dress or suit, the wonderful dining experience may not be remembered at all.

Basically, when something bad happens it overwrites the good portions of your memory. As we learned with bad days, your brain likes to focus on the negative stuff. To counteract this, the best thing you can do is remind yourself of the good parts of the experience as soon as possible. Think about everything good that happened instead of the one bad moment. Perhaps the bad moment is enough to deter you, but if not you can use it as an opportunity to remind your brain to store a positive memory instead of a negative one.